Many ailments of the gastrointestinal system in humans are caused at least in part by bacteria. Such bacteria include those of the genus Campylobacter, and particularly Helicobacter pylori. For example, Helicobacter pylori can cause bacterial infections on the mucosal surface of the gastrointestinal tract, particularly on the surface of the stomach. The chronic disorders of the gastrointestinal system that can be caused by bacteria include peptic ulcers, gastritis, and the like.
Once a patient is showing symptoms of a gastrointestinal disorder, several tests can be used to diagnose the disorder, including the diagnosis of a possible bacterial infection. In the past, various tests have been proposed for the detection of Helicobacter pylori. One such test that has gained wide spread popularity and has provided many advancements in the early detection of gastrointestinal disorders is disclosed in U.S. Pat. No. 4,748,113, which is incorporated herein by reference. In the '113 patent, the presence of Helicobacter pylori in a gastric sample is detected by testing for the presence of an enzyme, specifically urease, which is produced by Helicobacter pylori in large amounts.
Urease is known to convert urea into ammonium carbonate, which then decomposes into ammonia and carbon dioxide. Consequently, in the past, one test for detecting the presence of Helicobacter pylori included the steps of contacting a sample of gastric material with a composition containing urea and an indicator, namely a pH indicator that changes color when there is a rise in pH. If urease is present within the gastric material it breaks down the urea, which results in the formation of ammonia after further decomposition and causes the pH indicator to change color.
The gastric material that is collected from the patient is typically a biopsy specimen that is removed from the gastric mucosa at endoscopy by means of biopsy forceps. Typically, the tissue sample is inserted into a gel that contains urea and the indicator.
Although the above method has provided great advancements in the early detection of gastrointestinal disorders, the testing composition used to detect the presence of urease has a limited shelf life. In particular, the urea and other reagents contained within the composition can have a tendency to degrade over time. Consequently, once formulated, the testing composition should be used in a relatively short amount of time and is also typically refrigerated prior to use in order to prevent degradation.
In view of the above, a need currently exists for an improved testing composition and associated method for the detection of bacterial infections in the gastrointestinal tract of patients. More particularly, a need exists for a composition for detecting urease in gastric samples that has a prolonged shelf life.